1. Field of the Invention
This invention relates to a wire for welding which is adapted for use in automatic or semi-automatic welding of carbon steels or stainless steels, and more particularly, to a welding wire capable of improving feedabilities of the wire. The invention is applicable to both plated wires and uncovered or void wires.
2. Description of the Prior Art
Where welding wires are employed for automatic or semi-automatic welding, it is necessary to stably feed a wire from a spool or a wire accommodation pack to an arc-welding position. This welding wire is conveyed via the inside of a spring liner, such as a conduit cable, to the arc-welding portion. When the ease in the passage of a welding wire through a spring liner is defined as feedabilities of the wire, a welding wire exhibiting good feedabilities is able to pass through a long conduit cable by application of a small feeding force thereto. At welding spots wherein long conduit cables are frequently used such as in shipbuilding yards, it is essential that the feedabilities of a welding wire be good.
In welding spots where the feed system of welding wires is under severe conditions, welding over a long time causes skin or film dust to be deposited on feed rollers and in the inside of a spring liner, thereby inducing the feed failure of the wire. In order to improve the feedabilities of a welding wire, usual practice is to apply various types of lubricants having good slip properties to the surfaces of the wire. For improving slip properties, there has been proposed a wire for welding wherein the feedabilities of a wire are improved, for example, by applying, onto the surfaces of a welding wire, lubricating oils such as plant oils (e.g. palm oil) and animal oils (e.g. lard oil) and the particles of lubricating substances such as graphite and molybdenum disulfide (Japanese Laid-open Patent Application No. Hei 6-285678). When these lubricant oils and lubricating particles are applied onto a wire surface in appropriate amounts, the friction coefficient between the wire surface and the inner wall portions of a spring liner can be reduced, and thus, they show good lubricity, thereby improving the feedabilities of the wire.
Moreover, there are known other methods including a method (Japanese Laid-open Patent Application No. Hei 1-166898) wherein a sodium or potassium salt of a higher fatty acid having a great number of carbon atoms and having a linear or branched structure, e.g. stearic acid, oleic acid, linolic acid or linoleic acid is deposited on the surfaces of a wire, followed by final wire drawing and further application of a lubricant oil on the resultant wire to improve the feedabilities of the wire. Another method (Japanese Laid-open Patent Application No. Hei 2-284792) includes depositing, on wire surfaces, an oil lubricant containing sodium or potassium salts of carboxylic acids thereby improving the feedabilities of the wire. In both methods, the feedabilities of wires are improved by depositing, on wire surfaces, appropriate amounts of alkali metal salts of higher fatty acids and lubricating oils.
However, these known techniques have the following disadvantages. Initially, with the case of the welding wire (Japanese Laid-open Patent Application No. Hei 6-285678) wherein the feedabilities of the wire are improved by application of lubricating oils and lubricating substances made of molybdenum disulfide and graphite onto the wire surface, when the wire is subjected to welding operations over a long time, the lubricating substance is deposited on the inner walls of a spring line, thereby causing the liner to be clogged. Thus, the smooth feed of the wire is inconveniently impeded. This is for the reason that because the lubricating substance is not bonded to the wire surface, the lubricating substance readily separates from the wire surface.
On the other hand, in the method (Japanese Laid-open Patent Application No. Hei 1-166898) wherein a sodium or potassium salt of a higher fatty acid is deposited on a wire surface, followed by wire drawing and application of lubricating oils, and also in the method (Japanese Laid-open Patent Application No. Hei 2-284792) wherein an oil lubricant containing sodium or potassium salts of carboxylic acids is deposited on the surface of a wire, when welding is continued over a long time, like the first case, the alkali metal salt of a higher fatty acid and the lubricating oil are separated from the wire surface and deposited in the inside of a spring liner, thereby causing the spring liner to be clogged. Eventually, the feedabilities of the wire lower. Presumably, this is due to the fact that since the chain length of the hydrocarbon moiety of the carboxylate is too long, the bonding force between the wire surface and the lubricating oil is weak. This permits easy separation of the lubricating substance from the wire surface, thereby causing a deposit to be built up in the spring line. Moreover, the metal salts of higher fatty acids including sodium stearate serve as a good lubricant used for wire drawing, and such metal salts of higher fatty acids having a high molecular weight are apt to form a strong thick film on the surface of a wire. Thus, although the slip properties of the wire are improved, there is the fear that the wire may slip at feed rolls, thereby inducing a feeding failure. Especially, when a wire is plated, slipping may peel off the plated film.